Recently, demand has increased for an exhaust heat recovery boiler (there may be cases where it is called an HRSG or a heat recovery steam generator) which generates steam by collecting energy held by a combustion gas generated in a gas turbine and carries out power generation by using steam generated by a steam turbine.
FIG. 20 shows a duct wall 12 for an HRSG. A high-temperature and high-velocity gas 11 whose temperature is approx. 650° C. and velocity is 30 meters per second (m/s) is caused to flow from a gas turbine (not illustrated) into the duct wall 12, and heat thereof is thermally collected by a heat transfer tube bundle 13 installed inside the duct wall 12, and the gas whose temperature becomes comparatively low is exhausted through a smoke stack 14.
FIG. 21 is a side elevational view of the duct wall 12, which is observed in the direction of the arrow A shown in FIG. 20. The duct wall 12 occupies a greater part of the surface area of the entire HRSG, and reliability of the entire plant can be improved by making excellent the heat insulation and sound insulation performance of the duct wall 12.
FIG. 22 through FIG. 24 are sectional views in the direction parallel to the gas flow direction of the duct wall 12 of a prior art HRSG. The prior art duct wall 12 is generally structured so that, in order to insulate heat of the high temperature and high velocity gas 11 flowing in the interior of a duct, a heat insulating member 4 such as rock fibers, ceramic fibers, etc., is retained between the outer plate 2 at the outer side of the duct and the inner plate 3 at the inner side thereof. And, simultaneously, the heat insulating member 4 is used as a sound insulating material by utilizing a sound insulation function held by the heat insulating member 4.
The standard heat insulating structure of the duct wall 12 of the prior art HRSG shown in FIG. 22 (FIG. 22(a) is a sectional view of the duct wall 12, which is parallel to the gas flowing direction therein, and FIG. 22(b) is a partially enlarged view of FIG. 22(a) is such that a plurality of heat insulating members 4 are laminated and disposed between the outer plate (casing) 2 at the outer side of the duct wall 12 and the inner plate (inner lagging) 3 at the inner side of the duct into which a high temperature and high velocity gas 11 flows, the outer plate 2 and inner plate 3 are retained by stud bolts 5 and insulation pins 25 each having a function of fixing the heat insulating member 4, the inner plate 3 is mounted by providing a disk-shaped washer 36 and a nut 31 at the inner plate 3 side of the stud bolt 5 one end of which is supported on the outer plate 2, and a speed washer 26 is attached to the insulation pin 25 located at a conjunction part of respective layers of the heat insulating member 4, whereby the respective heat insulating members 4 are fixed.
In addition, such a construction of a prior art duct wall 12 has been known, which is shown in FIG. 23 (FIG. 23(a) is a sectional view of the duct wall 12 in the direction parallel to the gas flowing direction therein, and FIG. 23(b) is a view taken along the direction shown by the arrows A-A in FIG. 23(a)). The duct wall 12 shown in FIG. 23 is of a double heat insulating structure in which an intermediate member 6 is installed between the outer plate 2 and the inner plate 3, the outer plate 2 and intermediate member 6 are connected to each other by a stud bolt 5B, and the intermediate member 6 and inner plate 3 are connected to each other by a stud bolt 5A.
Further, a duct wall 12 has been known, which is shown in FIG. 24 (FIG. 24(a) is a sectional view of the duct wall 12 in the direction parallel to the gas flowing direction thereof, and FIG. 24(b) is a sectional view taken along the line A-A in FIG. 24(a)). The duct wall 12 shown in FIG. 24 is also of a double heat insulating structure, filed by the present applicant, in which an intermediate member 6 and a middle plate 9 are inserted between the outer plate 2 and the inner plate 3, the outer plate 2 and inner plate 3 are connected not by a single stud bolt 5, but the outer plate 2 and the intermediate member 6 are connected to each other by a stud bolt 5B, and the middle plate 9 and inner plate 3 are connected to each other by a stud bolt 5A.
Also, temperature distribution 100 between the inner plate 3 and outer plate 2 of the duct is shown on the left side of the sheet of FIG. 23(a) and FIG. 24(a).
In the structure of the duct wall 12 shown in FIG. 24, such a construction has generally been known in which, in order to insulate heat of a high temperature and high velocity gas 11 flowing in the interior of the duct wall 12, two layers of heat insulating members consisting of heat insulating members 4A and 4B respectively made of rock fibers, ceramic fibers, etc., are disposed between the inner plate 3 and the middle plate 9 and between the outer plate 2 and the middle plate 9. Since the heat insulating members 4A and 4B have a sound insulating function, the duct wall 12 in which the heat insulating members 4A and 4B are placed between the outer plate 2 and the inner plate 3 can bring about a sound insulating structure. Such a connection method is generally employed for the outer plate 2 and the inner plate 3, in which the heat insulating members 4A and 4B are placed therebetween, and are usually connected to each other by means of stud bolts 5A and 5B and nuts 7A and 7B.
However, although an acoustic absorption structure of double layers of heat insulation of the duct wall 12 shown in FIG. 24 has excellent sound block-out performance, the weight is contrarily increased, and there are many disadvantages such as an increase in processing, working and designing costs, etc. Therefore, there was a necessity in newly developing a cost-suppressed heat insulation and sound insulation structure.
In the meantime, transmission sound from the interior of an HRSG into the exterior thereof is measured as noise. Where no silencer is provided in the interior of the HRSG, since an exhaust gas of a gas turbine internally exists in the HRSG without any acoustic energy of the turbine exhaust gas (high temperature and high velocity gas) being dampening, it is necessary to improve the sound block-out performance of the HRSG wall as a sound insulating countermeasure.
Sound transmitting through the duct wall 12 is classified into two types which are air-borne sound and solid-borne sound, wherein the sound insulation performance of the duct wall 12 is determined by a sound-borne loss of the outer plate 2, inner plate 3 and heat insulating member 4, wherein it is considered that almost all of the transmission sound is solid-borne sound which is transmitted from the inner plate 3 to the outer plate 2 via the stud bolts 5.
The duct wall structure disclosed in FIG. 22 through FIG. 24 is based on a method for dampening solid transmission sound by lengthening the channel of solid transmission sound, wherein the intermediate member 6 is disposed between the inner plate 3 and the outer plate 2, the inner plate 3 and the intermediate member 6 are connected to each other by means of stud bolts 5A and nuts 7A, and the outer plate 2 and the intermediate member 6 are further connected to each other by means of stud bolts 5B and nuts 7B. However, such a structure is general in terms of insulating the solid transmission sound, and a structure similar thereto is disclosed in Japanese Unexamined Patent Publications Nos. Sho-51-143915 and Hei-11-351488.
Further, a vibration deadening washer 8 of a structure in which a vibration deadening material 8b shown in FIG. 2 is placed and nipped between two plate materials 8a has been known as a vibration deadening and sound insulating material for buildings. A general example thereof is disclosed in Japanese Unexamined Patent Publications Nos. Sho-52-92501, Hei-9-279717 and 2000-27333, etc.
Patent Document 1 Japanese Unexamined Patent Application No. Sho-51-143915
Patent Document 2 Japanese Unexamined Patent Application No. Hei-11-351488
Patent Document 3 Japanese Unexamined Patent Application No. Sho-52-92501
Patent Document 4 Japanese Unexamined Patent Application No. Hei-9-279717
Patent Document 5 Japanese Unexamined Patent Application No. 2000-27333